Electronic Switch having an In-Line Power Supply

ABSTRACT

A two-wire smart load control device, such as an electronic switch, for controlling the power delivered from a power source to an electrical load comprises a relay for conducting a load current through the load and an in-line power supply coupled in series with the relay for generating a supply voltage across a capacitor when the relay is conductive. The power supply controls when the capacitor charges asynchronously with respect to the frequency of the source. The capacitor conducts the load current for at least a portion of a line cycle of the source when the relay is conductive. The load control device also comprises a bidirectional semiconductor switch, which is controlled to minimize the inrush current conducted through the relay. The bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the capacitor of the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of commonly-assigned U.S.patent application Ser. No. 12/751,324, filed Mar. 31, 2010, entitledSMART ELECTRONIC SWITCH FOR LOW-POWER LOADS, which is a non-provisionalapplication of commonly-assigned U.S. Provisional Application Ser. No.61/172,511, filed Apr. 24, 2009, entitled SMART LOAD CONTROL DEVICEHAVING A ZERO-CURRENT OFF STATE, and U.S. Provisional Application Ser.No. 61/226,990, filed Jul. 20, 2009, entitled SMART ELECTRONIC SWITCHFOR LOW-POWER LOADS, the entire disclosures of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to load control devices for control of thepower delivered from an alternating-current (AC) power source to anelectrical load, and more particularly, to a “smart” two-wire electronicswitch having a controller, a latching relay, and a power supply thatprovides substantially all of the line voltage of the AC power source tothe load and draws current through the load in a manner that does notresult in inappropriate operation of the load.

2. Description of the Related Art

Typical load control devices are operable to control the amount of powerdelivered to an electrical load, such as a lighting load or a motorload, from an alternating-current (AC) power source. Wall-mounted loadcontrol devices are adapted to be mounted to standard electricalwallboxes. A dimmer switch comprises a controllably conductive device(e.g., a bidirectional semiconductor switch, such as, a triac), which iscoupled in series between the power source and the load. Thecontrollably conductive device is controlled to be conductive andnon-conductive for portions of a half cycle of the AC power source tothus control the amount of power delivered to the load (e.g., using aphase-control dimming technique). A “smart” dimmer switch (i.e., adigital dimmer switch) comprises a microprocessor (or similarcontroller) for controlling the semiconductor switch and a power supplyfor powering the microprocessor. In addition, the smart dimmer switchmay comprise a memory, a communication circuit, and a plurality oflight-emitting diodes (LEDs) that are all powered by the power supply.

An electronic switch (i.e., a digital switch) comprises a controllablyconductive device (such as a relay or a bidirectional semiconductorswitch), a microprocessor, and a power supply. In contrast to a smartdimmer switch, the controllably conductive device of an electronicswitch is not controlled using the phase-controlled dimming technique,but is controlled to be either conductive or non-conductive during eachhalf cycle of the AC power source to thus toggle the electrical load onand off. Often, wall-mounted electronic switches do not require aconnection to the neutral side of the AC power source (i.e., theelectronic switch is a “two-wire” device). This is particularly usefulwhen the electronic switch is installed in a retro-fit installation(i.e., to replace an existing switch or load control device in anelectrical wallbox in which there is no neutral connection).

In order to charge, the power supply of a two-wire electronic switchmust develop an amount of voltage across the power supply. As a result,not all of the AC line voltage of the AC power source is available topower the electrical load and the electrical load may not operateproperly. For example, if the electrical load is a lighting load, thelighting load may not be illuminated to the maximum possible intensity.In addition, the power supply must draw current through the controlledelectrical load in order to charge, which may cause problems for sometypes of electrical loads. For example, when the electrical load is alighting load, the magnitude of the power supply current must not begreat enough to cause the lighting load to illuminate or to flicker.Further, some electrical loads, such as compact fluorescent lamps, donot conduct sinusoidal currents, and as a result, current cannot beconducted through these electrical loads during certain portions of theline cycle of the AC power source.

Therefore, there exists a need for an electronic switch that has acontroller for turning the load on and off and a single power supplythat operates in a manner that does not result in inappropriateoperation of the load.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a two-wireelectronic switch adapted to be coupled between an AC power source andan electrical load for turning the electrical load on and off comprisesa controllably conductive device adapted to be coupled in serieselectrical connection between the source and the load, a controlleroperatively coupled the controllably conductive device for controllingthe controllably conductive, an output capacitor operable to develop tothe DC supply voltage for powering the controller, and an in-line powersupply that controls when the output capacitor charges asynchronouslywith respect to the frequency of the AC power source, such that thein-line power supply is operable to start and stop charging at any timeduring each half cycle. The controllably conductive device is adapted toconduct a load current through the load when the controllably conductivedevice is conductive. The controller renders the controllably conductivedevice conductive and non-conductive to turn the load on and off,respectively. The in-line power supply is coupled in series with thecontrollably conductive device, and further coupled to the outputcapacitor for controlling when the output capacitor charges in order togenerate the DC supply voltage across the output capacitor when thecontrollably conductive device is conductive. A voltage developed acrossthe in-line power supply when the output capacitor is charging has asubstantially small magnitude as compared to a peak voltage of an ACline voltage of the AC power source. The output capacitor is adapted toconduct the load current for at least a portion of a line cycle of theAC power source when the controllably conductive device is conductive.The power supply starts and stops charging the output capacitor at leastonce during each half cycle of the AC power source.

In addition, a power supply for an electronic switch that comprises acontrollably conductive device adapted to be coupled between an AC powersource and an electrical load for turning the electrical load on and offis also described herein. The electronic switch comprises an outputcapacitor operable to develop to a DC supply voltage, a bidirectionalsemiconductor switch adapted to be coupled in series with thecontrollably conductive device and in parallel with the outputcapacitor, and a control circuit coupled to the bidirectionalsemiconductor switch for rendering the bidirectional semiconductorswitch conductive and non-conductive. The output capacitor is operableto charge when the bidirectional semiconductor switch is non-conductive.The control circuit is responsive to the magnitude of the DC supplyvoltage to render the bidirectional semiconductor switch conductive whenthe magnitude of the DC supply voltage reaches a maximum DC supplyvoltage threshold and to render the bidirectional semiconductor switchnon-conductive when the magnitude of the DC supply voltage drops to aminimum DC supply voltage threshold. A voltage developed across thepower supply when the output capacitor is charging has a substantiallysmall magnitude as compared to a peak voltage of an AC line voltage ofthe AC power source when the output capacitor is charging. The powersupply controls when the output capacitor charges asynchronously withrespect to the frequency of the AC power source, such that the in-linepower supply is to start and stop charging at any time during each halfcycle. The power supply starts and stops charging the output capacitorat least once during each half cycle of the AC power source.

According to another embodiment of the present invention, a two-wireelectronic switch for controlling the power delivered from an AC powersource to an electrical load comprises a latching relay adapted to becoupled in series electrical connection between the source and the load,a controller, an output capacitor operable to develop a DC supplyvoltage for powering the controller, and an in-line power supply coupledin series with the relay and further coupled to the output capacitor forgenerating the DC supply voltage across the output capacitor when therelay is conductive. The latching relay conducts a load current throughthe load when the relay is conductive. The controller is operativelycoupled to the relay for controlling the relay to be conductive andnon-conductive to turn the load on and off, respectively. The outputcapacitor is adapted to conduct the load current for at least a portionof a line cycle of the AC power source when the relay is conductive. Therelay is rendered non-conductive in response to an over-temperaturecondition in the electronic switch (e.g., in the power supply).

According to yet another embodiment of the present invention, a two-wireelectronic switch for controlling the power delivered from an AC powersource to an electrical load comprises a latching relay adapted to becoupled in series electrical connection between the source and the loadfor turning the load on and off, a first bidirectional semiconductorswitch coupled in parallel electrical connection with the relay, and acontroller operatively coupled to the relay and a control input of thefirst bidirectional semiconductor switch. The controller turns on theload by first rendering the first bidirectional semiconductor switchconductive and then rendering the relay conductive, and turns off theload by first rendering the relay non-conductive and then rendering thefirst bidirectional semiconductor switch non-conductive. The electronicswitch further comprises an output capacitor operable to develop a DCsupply voltage for powering the controller, and an in-line power supplycoupled in series electrical connection with the relay, such that thefirst bidirectional semiconductor switch is coupled in parallel with theseries combination of the relay and the power supply. The in-line powersupply is further coupled to the output capacitor for generating the DCsupply voltage across the output capacitor when the relay is conductive.The output capacitor is adapted to conduct the load current for at leasta portion of a line cycle of the AC power source when the relay isconductive. The first bidirectional semiconductor switch is renderedconductive in response to an over-current condition in the outputcapacitor of the power supply. In addition, the power supply may furthercomprise a second bidirectional semiconductor switch coupled in serieswith the relay and in parallel with the output capacitor, such that theoutput capacitor is operable to charge when the relay is conductive andthe second bidirectional semiconductor switch is non-conductive.

According to another embodiment of the present invention, a two-wireelectronic switch for controlling the power delivered from an AC powersource to an electrical load comprises: (1) a latching relay adapted tobe coupled in series electrical connection between the source and theload for turning the load on and off; (2) a first bidirectionalsemiconductor switch coupled in parallel electrical connection with therelay, the first bidirectional semiconductor switch comprising a controlinput; (3) a controller operatively coupled to the relay and the controlinput of the first bidirectional semiconductor switch, the controlleroperable to turn on the load by first rendering the first bidirectionalsemiconductor switch conductive and then rendering the relay conductive,the controller operable to turn off the load by first rendering therelay non-conductive and then rendering the first bidirectionalsemiconductor switch non-conductive; (4) an output capacitor operable todevelop a DC supply voltage for powering the controller; and (5) anin-line power supply coupled in series electrical connection with therelay, such that the first bidirectional semiconductor switch is coupledin parallel with the series combination of the relay and the powersupply. The in-line power supply is further coupled to the outputcapacitor for generating the DC supply voltage across the outputcapacitor when the relay is conductive. The power supply comprises asecond bidirectional semiconductor switch coupled in series with therelay and in parallel with the output capacitor, such that the outputcapacitor is operable to charge when the relay is conductive and thesecond bidirectional semiconductor switch is non conductive. The firstbidirectional semiconductor switch is rendered conductive in response toan over-current condition in the output capacitor of the power supply,and the relay is rendered non-conductive in response to anover-temperature condition in the power supply.

According to another aspect of the present invention, a two-wireelectronic switch for controlling the power delivered from an AC powersource to an electrical load comprises a latching relay adapted to becoupled in series electrical connection between the source and the loadfor turning the load on and off, an output capacitor operable to developa DC supply voltage, an in-line power supply, and a controller operableto measure a charging time required to charge the output capacitor, andto determine if an overload condition is occurring if the length of thecharging time is less than a predetermined charging time threshold. Thein-line power supply is coupled in series electrical connection with therelay, and further coupled to the output capacitor for generating the DCsupply voltage across the output capacitor when the relay is conductive.The power supply comprises a bidirectional semiconductor switch coupledin series with the relay and in parallel with the output capacitor, suchthat the output capacitor is operable to charge when the relay isconductive and the bidirectional semiconductor switch is non conductive.The bidirectional semiconductor switch is rendered conductive when themagnitude of the DC supply voltage reaches a maximum DC supply voltagethreshold and rendered non-conductive when the magnitude of the DCsupply voltage drops to a minimum DC supply voltage threshold. Theoutput capacitor is adapted to conduct the load current for at least aportion of a line cycle of the AC power source when the relay isconductive.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail in the followingdetailed description with reference to the drawings in which:

FIG. 1 is a simplified diagram of a radio-frequency (RF) lightingcontrol system comprising a two-wire electronic switch and two remotevacancy sensors according to a first embodiment of the presentinvention;

FIG. 2 is a simplified block diagram of the two-wire electronic switchof FIG. 1;

FIG. 3 is a simplified schematic diagram of an in-line on-state powersupply of the two-wire electronic switch of FIG. 2;

FIG. 4A is a simplified diagram of waveforms illustrating the operationof the power supply of FIG. 3 showing an asynchronous charging currentconducted through an output capacitor of the power supply;

FIG. 4B is a simplified diagram of waveforms illustrating the operationof the power supply of FIG. 3 showing a synchronous charging currentconducted through the output capacitor of the power supply;

FIG. 5 is a simplified schematic diagram of a latching relay, abidirectional semiconductor switch, a drive circuit, and the in-lineon-state power supply of the two-wire electronic switch of FIG. 2;

FIG. 6 is a simplified flowchart of a button procedure executed by acontroller of the electronic switch of FIG. 2;

FIG. 7 is a simplified flowchart of a received message procedureexecuted by the controller of the electronic switch of FIG. 2;

FIG. 8 is a simplified flowchart of a relay timer procedure executed bythe controller of the electronic switch of FIG. 2;

FIG. 9 is a simplified flowchart of a bidirectional semiconductor switch(BSS) timer procedure executed by the controller of the electronicswitch of FIG. 2; and

FIG. 10 is a simplified flowchart of an overload detection procedureexecuted by the controller of the electronic switch of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 1 is a simple diagram of a radio-frequency (RF) lighting controlsystem 100 comprising a two-wire electronic switch 110, a keypad 120,and two remote occupancy sensors 130 according to a first embodiment ofthe present invention. The electronic switch 110 and the keypad 120 areadapted to be wall-mounted in standard electrical wallboxes.Alternatively, the electronic switch 110 and the keypad 120 could beimplemented as table-top control devices. In addition, the electronicswitch 110 may comprise a controllable plug-in module adapted to beplugged into an electrical receptacle or a controllable screw-in moduleadapted to be screwed into the electrical socket (e.g., an Edisonsocket) of a lamp.

The electronic switch 110 comprises a hot terminal H and a switched hotterminal SH and is adapted to be coupled in series electrical connectionbetween an AC power source 102 (e.g., 120 V_(AC)@60 Hz or 240 V_(AC)@50Hz) and a lighting load 104 for controlling the power delivered to thelighting load. The electronic switch 110 generates a switched hotvoltage V_(SH) at the switched hot terminal SH. The electronic switch110 comprises a control actuator 112 (i.e., a control button) fortoggling (i.e., turning off and on) the lighting load 104, and a visualindicator 114 for providing feedback of whether the lighting load is onor off. The electronic switch 110 is also operable to turn the lightingload 104 off in response to digital messages received from the keypad120 and the occupancy sensors 130 via RF signals 106.

The keypad 120 is coupled to the hot and neutral connections of the ACpower source 102 via a hot terminal H′ and a neutral terminal N,respectively. The keypad 120 comprises an on button 122 and an offbutton 124 for turning the lighting load 104 on and off, respectively.The keypad 120 is operable to transmit a digital message including an“on” command to the electronic switch 110 in response to an actuation ofthe on button 122, and to transmit a digital message including an “off”command to the electronic switch in response to an actuation of the offbutton 124. The keypad 120 further comprises visual indicators 126provided on the button 122, 124 for providing feedback of whether thelighting load 104 is on or off.

The occupancy sensors 130 are removably mountable to a ceiling or awall, for example, in the vicinity of (i.e., a space around) thelighting load 104 controlled by the electronic switch 110. The occupancysensors 130 are operable to detect the presence of an occupant in thespace (i.e., an occupancy condition) and the absence of the occupancy(i.e., a vacancy condition) in the vicinity of the lighting load 104.The occupancy sensors 130 may be spaced apart to detect occupancyconditions in different areas of the vicinity of the lighting load 104.The occupancy sensors 130 and the electronic switch 110 operate to turnon the lighting load when one of the occupancy sensors detects that anoccupant has entered the space (i.e., at least one sensor detects anoccupancy condition) and then to turn off the lighting load when bothoccupancy sensors detect that the user has left the space (i.e., bothsensors detect vacancy conditions).

Alternatively, the occupancy sensors 130 could be implemented as vacancysensors. A vacancy sensor only operates to turn off the lighting load104 when the vacancy sensor detects a vacancy in the space. Therefore,when using vacancy sensors, the lighting load 104 must be turned onmanually (e.g., in response to a manual actuation of the controlactuator 112). Examples of wireless battery-powered occupancy sensorsare described in greater detail in U.S. patent application Ser. No.12/203,500, filed Sep. 3, 2008, entitled BATTERY-POWERED OCCUPANCYSENSOR, the entire disclosure of which is hereby incorporated byreference.

The occupancy sensors 130 each include an internal detector (not shown),e.g., a pyroelectric infrared (PIR) detector. The internal detector ishoused in an enclosure 132, which has a lens 134 for directing infraredenergy from an occupant in the space to the internal detector forsensing the occupancy condition in the space. The occupancy sensors 130are operable to process the output of the internal detector to determinewhether an occupancy condition or a vacancy condition is presentlyoccurring in the space, for example, by comparing the output of the PIRdetector to a predetermined occupancy voltage threshold. Alternatively,the internal detector could comprise an ultrasonic detector, a microwavedetector, or any combination of PIR detectors, ultrasonic detectors, andmicrowave detectors. The occupancy sensors 130 each operate in an“occupied” state or a “vacant” state in response to the detections ofoccupancy or vacancy conditions, respectively, in the space. If one ofthe occupancy sensors 130 is in the vacant state and the occupancysensor determines that the space is occupied, the occupancy sensorchanges to the occupied state. Similarly, the occupancy sensor 130changes to the vacant state, if the occupancy sensor is in the occupiedstate and the occupancy sensor determines that the space is unoccupied.

During a setup procedure of the RF lighting control system 100, theelectronic switch 110 and the keypad 120 may be assigned to (i.e.,associated with) the occupancy sensors 130. The setup and configurationof a lighting control system including occupancy sensors is described ingreater detail in U.S. patent application Ser. No. 12/371,027, filedFeb. 13, 2009, entitled METHOD AND APPARATUS FOR CONFIGURING A WIRELESSSENSOR, the entire disclosure of which is hereby incorporated byreference.

The occupancy sensors 130 transmit digital messages wirelessly via theRF signals 106 in response to the present state of the occupancy sensors(i.e., whether an occupancy condition or a vacancy condition has beendetected). The electronic switch 110 turns the lighting load 104 on andoff in response to the digital messages received via the RF signals 106.A digital message transmitted by the remote occupancy sensors 130 mayinclude a command and identifying information, for example, a serialnumber associated with the transmitting occupancy sensor. The electronicswitch 110 is responsive to messages containing the serial numbers ofthe remote occupancy sensors 130 to which the electronic switch isassigned. The operation of the RF lighting control system 100 isdescribed in greater detail in U.S. patent application Ser. No.12/203,518, filed Sep. 3, 2008, entitled RADIO-FREQUENCY LIGHTINGCONTROL SYSTEM WITH OCCUPANCY SENSING, the entire disclosure of which ishereby incorporated by reference.

The commands included in the digital messages transmitted by theoccupancy sensors 130 may comprise an occupied command (e.g., anoccupied-take-action command or an occupied-no-action command) or avacant command. When the lighting load 104 is off, the electronic switch110 is operable to turn on the lighting load in response to receiving afirst occupied-take-action command from any one of the occupancy sensors130. The electronic switch 110 is operable to turn off the lighting load104 in response to the last vacant command received from those occupancysensors 130 from which the occupancy sensor received eitheroccupied-take-action or occupied-no-action commands. For example, if theoccupancy sensors 130 both transmit occupied-take-action commands to theelectronic switch 110, the electronic switch will not turn off thelighting load 104 until subsequent vacant commands are received fromboth of the occupancy sensors.

Each occupancy sensor 130 also comprises an internal ambient lightdetector (not shown), e.g., a photocell, for detecting the level ofambient light around the occupancy sensor. The occupancy sensor 130measures the ambient light level when an occupancy condition is firstdetected and compares the ambient light level to a predetermined ambientlight level threshold. If the measured ambient light level is less thanthe predetermined level when an occupancy condition is first detected byone of the occupancy sensors 130, the occupancy sensor transmits theoccupied-take-action command to the electronic switch 110. On the otherhand, if the measured ambient light level is greater than thepredetermined level when an occupancy condition is first detected, theoccupancy sensor 130 transmits the occupied-no-action command to theelectronic switch 110. Accordingly, the electronic switch 110 does notturn on the lighting load 104 if the ambient light level in the space issufficient.

The occupancy sensors 130 are each characterized by a predeterminedoccupancy sensor timeout period T_(TIMEOUT), which provides some delayin the adjustment of the state of the occupancy sensor, specifically, inthe transition from the occupied state to the vacant state. Thepredetermined timeout period T_(TIMEOUT) denotes the time between thelast detected occupancy condition and the transition of the occupancysensor 130 from the occupied state to the vacant state. Thepredetermined occupancy sensor timeout period T_(TIMEOUT) may beuser-selectable, for example, ranging from approximately five to thirtyminutes. Each occupancy sensor 130 will not transmit a vacant commanduntil the occupancy sensor timeout period T_(TIMEOUT) has expired. Eachoccupancy sensor 130 maintains an occupancy timer to keep track of thetime that has expired since the last detected occupancy condition. Theoccupancy sensors 130 periodically restart the occupancy timers inresponse to detecting a continued occupancy condition. Accordingly, theoccupancy sensors 130 do not change to the vacant state, and thelighting load 104 is not turned off, in response to brief periods of alack of movement of the occupant in the space. If the occupancy sensor130 fails to continue detecting the occupancy conditions, the occupancysensor uses the occupancy timer to wait for the length of the occupancysensor timeout period T_(TIMEOUT), after which the occupancy sensorchanges to the vacant state and transmits a vacant command to theelectronic switch 110.

FIG. 2 is a simplified block diagram of the electronic switch 110. Theelectronic switch 110 comprises a controllably conductive device (e.g.,a latching relay 210) connected in series electrical connection betweenthe hot terminal H and the switched hot terminal SH. The relay 210conducts a load current I_(L) from the AC power source 102 to thelighting load 104 when the relay is closed (i.e., conductive). The loadcurrent I_(L) may have, for example, a magnitude of approximately fiveamps depending upon the type of lighting load 104. The electronic switch110 further comprises a bidirectional semiconductor switch 212 coupledin parallel electrical connection with the relay 210 for minimizing theinrush current conducted through the relay 210 (and thus limiting anyarcing that may occur at the contacts of the relay) when the lightingload 104 is first turned on. Specifically, the bidirectionalsemiconductor switch 212 is controlled to be conductive before the relay210 is rendered conductive when the electronic switch 110 is turning onthe lighting load 104, and is controlled to be non-conductive after therelay is rendered non-conductive when the electronic switch is turningof the lighting load. The bidirectional semiconductor switch 212 maycomprise, for example, a triac, a field-effect transistor (FET) in arectifier bridge, two FETs in anti-series connection, one or moresilicon-controlled rectifiers (SCRs), one or more insulated-gate bipolarjunction transistors (IGBTs), or any other suitable type ofbidirectional semiconductor switch.

The relay 210 and the bidirectional semiconductor switch 212 areindependently controlled by a controller 214. For example, thecontroller 214 may be a microcontroller, but may alternatively be anysuitable processing device, such as a programmable logic device (PLD), amicroprocessor, an application specific integrated circuit (ASIC), or afield-programmable gate array (FPGA). The controller 214 is coupled toSET and RESET terminals (e.g., SET and RESET coils) of the relay 210 forcausing the relay to become conductive and non-conductive, respectively.Specifically, the controller 214 generates a relay-set control signalV_(RLY-SET) for driving the SET coil and a relay-reset control signalV_(RLY-RESET) for driving the RESET coil. The controller 214 alsoprovides a BSS-drive control signal V_(BSS-DRIVE) to the a control inputof the bidirectional semiconductor switch 212 via a gate drive circuit216 for rendering the bidirectional semiconductor switch conductive.

The electronic switch 110 comprises two power supplies: an on-state(in-line) power supply 220 and an off-state power supply 222. Both powersupplies 220, 222 operate to generate a DC supply voltage V_(CC) (e.g.,having an average magnitude of approximately five volts) across anoutput capacitor C_(OUT) (e.g., having a capacitance of approximately680 μF). The controller 214 and other low-voltage circuitry of theelectronic switch 110 are powered from the DC supply voltage V_(CC). Thebidirectional semiconductor switch 212 is coupled in series electricalconnection with the parallel combination of the relay 210 and theon-state power supply 220. The on-state power supply 220 operates togenerate the DC supply voltage V_(CC) when the relay 210 is closed andthe lighting load 104 is on as will be described in greater detailbelow. The off-state power supply 222 is coupled in parallel electricalconnection with the relay 210 and the bidirectional semiconductor switch212 and operates to generate the DC supply voltage V_(CC) when the relay210 is open and the lighting load 104 is off. Since the output capacitorC_(OUT) is referenced to the circuit common of the on-state power supply220, the off-state power supply 222 may comprise an isolated powersupply.

The controller 214 receives inputs from a momentary tactile (i.e.,mechanical) switch S224, which temporarily closes in response toactuations of the control actuator 112 of the electronic switch 110. Theseries combination of the switch S224 and a resistor S226 (e.g., havinga resistance of approximately 15 kΩ) is coupled between the DC supplyvoltage V_(CC) and the circuit common. When the control actuator 112 isactuated and the switch S224 is temporarily closed, the input port ofthe controller 214 is pulled down towards circuit common, thus signalingto the controller 214 that the switch S224 has been actuated.Accordingly, the controller 214 is operable to control the relay 210 andthe bidirectional semiconductor switch 212 to toggle the lighting load104 on and off in response to actuations of the switch S224. Thecontroller 214 is further operable to control the visual indicator 114to be illuminated when the lighting load 104 is on and not illuminatedwhen the lighting load is off.

The controller 214 is also coupled to a memory 228 for storage of theserial number of the keypad 120 and the occupancy sensors 130 to whichthe electronic switch 110 is assigned. The memory 228 may be implementedas an external integrated circuit (IC) or as an internal circuit of thecontroller 214. The electronic switch 110 further comprises an RFtransceiver 230 and an antenna 232 for transmitting and receiving the RFsignals 106 with the keypad 120 and the occupancy sensors 130. Thecontroller 214 is operable to control the relay 210 and thebidirectional semiconductor switch 212 in response to the digitalmessages received via the RF signals 106. Examples of the antenna 232for wall-mounted load control devices, such as the electronic switch110, are described in greater detail in U.S. Pat. No. 5,982,103, issuedNov. 9, 1999, and U.S. patent application Ser. No. 10/873,033, filedJun. 21, 2006, both entitled COMPACT RADIO FREQUENCY TRANSMITTING ANDRECEIVING ANTENNA AND CONTROL DEVICE EMPLOYING SAME, the entiredisclosures of which are hereby incorporated by reference.

Alternatively, the electronic switch 110 could simply comprise an RFreceiver for only receiving digital messages from the keypad 120 and theoccupancy sensors 130 via the RF signals 106. In addition, theelectronic switch 110 could alternatively comprise an infrared (IR)receiver for receipt of IR signals, a wired communication circuit forconnection to a wired communication link, a power-line carrier (PLC)communication circuit, or another type of communication circuit.Examples of lighting control system including other types ofcommunication circuits are described in greater detail in U.S. Pat. No.6,545,434, issued Apr. 8, 2003, entitled MULTI-SCENE PRESET LIGHTINGCONTROLLER; U.S. Pat. No. 7,423,413, issued Sep. 8, 2009, entitled POWERSUPPLY FOR A LOAD CONTROL DEVICE; and U.S. patent application Ser. No.11/447,431, filed Jun. 6, 2006, entitled SYSTEM FOR CONTROL OF LIGHTSAND MOTORS; the entire disclosures of which are hereby incorporated byreference.

The on-state power supply 220 generates the DC supply voltage V_(CC)while allowing the electronic switch 110 to provide substantially all ofthe AC line voltage to the lighting load 104 when the lighting load ison. When the output capacitor C_(OUT) is charging through the on-statepower supply 220 (while the relay 210 is conductive), the voltagedeveloped across the on-state power supply has a substantially smallmagnitude (e.g., approximately the DC supply voltage V_(CC), i.e.,approximately five volts) as compared to the peak voltage of the AC linevoltage of the AC power source 102. In other words, the on-state powersupply 220 imposes a substantially low voltage drop as compared to thepeak voltage of the AC line voltage of the AC power source 102, suchthat the voltage provided to the lighting load 104 (i.e., switched hotvoltage V_(SH)) is only slightly smaller when the output capacitorC_(OUT) is charging. For example, the peak voltage of the AC linevoltage is approximately 340 volts when the RMS voltage of the AC powersource 102 is 240 V_(AC), while the voltage developed across theon-state power supply 220 is equal to approximately the DC supplyvoltage V_(CC) (i.e., approximately five volts) for only a portion ofeach half cycle of the AC power source 102.

The on-state power supply 220 conducts a charging current I_(CHRG) (FIG.3) through the output capacitor C_(OUT) for charging the outputcapacitor. The output capacitor C_(OUT) is adapted to conduct the loadcurrent I_(L) for at least a portion of a line cycle of the AC powersource 102 when the relay is conductive. Accordingly, the chargingcurrent I_(CHRG) is equal to the load current I_(L) for at least aportion of a line cycle of the AC power source 102 when the relay isconductive. The on-state power supply 220 is able to operate properlywhen the lighting load 104 is a low-power load, e.g., having a powerrating down to approximately 25 W (and a voltage rating of 240 V_(AC)).In other words, the on-state power supply 220 is operable toappropriately charge the output capacitor C_(OUT) to keep the controller214 powered when the load current I_(L) has a magnitude as low asapproximately 100 mA.

Since the lighting load 104 may cause the load current I_(L) of theon-state power supply 220 to be a non-sinusoidal current (e.g., if thelighting is a compact fluorescent lamp), the output capacitor C_(OUT)may not be able to conduct the charging current I_(CHRG) through thelighting load during certain portions of the line cycle of the AC powersource 102. Accordingly, the on-state power supply 220 controls when theoutput capacitor C_(OUT) is able to charge in a manner that isasynchronous with respect to the frequency of the AC line voltage of theAC power source 102, such that the power supply is operable to start andstop charging at any time during each half cycle (i.e., at any timebetween the beginning and the end of the half cycle). Specifically, theon-state power supply 220 is operable to begin charging the outputcapacitor C_(OUT) when the magnitude of the DC supply voltage V_(CC)drops to a minimum supply voltage V_(CC-MIN) (e.g., approximately fivevolts). However, the output capacitor C_(OUT) may not begin charginguntil the output capacitor C_(OUT) is able to conduct the load currentI_(L) through the lighting load 104 (i.e., if the load current I_(L) isnon-sinusoidal). The on-state power supply 220 always stops chargingwhen the magnitude of the DC supply voltage rises to a maximum supplyvoltage V_(CC-MAX) (e.g., approximately six volts). When the lightingload 104 is a resistive load, such as an incandescent lamp (i.e., theload current I_(L) is sinusoidal), the charging current I_(CHRG) of theon-state power supply 220 may be asynchronous with respect to thefrequency of the AC line voltage (as shown FIG. 4A). Alternatively, ifthe lighting load 104 conducts a non-sinusoidal load current I_(L), thecharging current I_(CHRG) may be synchronous with respect to the linevoltage frequency (as shown in FIG. 4B).

In order to minimize visible flickering in the lighting load 104, theon-state power supply 220 draws current from the AC power source 102 atleast once every half cycle of the AC power source 102. Accordingly, thetime period between any two consecutive pulses of the charging currentI_(CHRG) is less than the period T_(HC) of a half cycle (e.g.,approximately ten milliseconds for a 50-Hz power source), and thus thefrequency of the pulses of the charging current I_(CHRG) is greater thanthe twice the line voltage frequency (e.g., approximately 100 Hz), so asavoid visible flickering in the lighting load 104. The time periodbetween any two consecutive pulses of the charging current I_(CHRG) maybe approximately equal to the period T_(HC) of a half cycle if thecharging current I_(CHRG) is synchronous with respect to the linevoltage frequency (as shown in FIG. 4B).

The controller 214 is operable to monitor the operation of the on-statepower supply 220 in order to determine the appropriate times to performactions that require larger amounts of current to be drawn from theoutput capacitor C_(OUT), such as energizing the coils of the relay 210.The on-state power supply 220 provides to the controller 214 a feedbackcontrol signal V_(FB), which is representative of whether the outputcapacitor C_(OUT) is charging or not as will be described in greaterdetail below. The controller 214 may be operable to energize the SET andRESET coils of the relay 210 immediately after the output capacitorC_(OUT) stops charging, i.e., when the magnitude of the DC supplyvoltage V_(CC) is equal to the maximum supply voltage V_(CC-MAX) and themaximum amount of voltage is available to energize the coils.

FIG. 3 is a simplified schematic diagram of the in-line power supply 220according to the first embodiment of the present invention. The on-statepower supply 220 includes a bidirectional semiconductor switch 310comprising, for example, two FETs Q312, Q314 coupled in anti-seriesconnection. The on-state power supply 220 also comprises a full-waverectifier bridge that includes the body diodes of the two FETs Q312,Q314 in addition to two diodes D316, D318, which are all coupled to theoutput capacitor C_(OUT), for allowing the output capacitor to chargefrom the AC power source 102 through the lighting load 104. Therectifier bridge has AC terminals coupled in series between the switchedhot terminal SH and the relay 210, and DC terminals for providing arectified voltage V_(RECT). The output capacitor C_(OUT) is coupled inseries between the DC terminals of the rectifier bridge, such that theoutput capacitor is able to charge from the AC power source 102 throughthe rectifier bridge and the lighting load 104. Theanti-series-connected FETs Q312, Q314 are coupled in parallel electricalconnection with the AC terminals of the rectifier bridge, such that theFETs are operable to conduct the load current I_(L) from the AC powersource 102 to the lighting load 104 when the FETs are conductive, andthe output capacitor C_(OUT) is operable to conduct the load currentI_(L) when the FETs are non-conductive.

The output capacitor C_(OUT) is also coupled in series with anover-current detect resistor R320 (e.g., having a resistance ofapproximately 0.1Ω) and a positive-temperature-coefficient (PTC)thermistor R322, which allow for the detection of fault conditions(e.g., an over-current or an over-temperature condition in theelectronic switch 110), as will be described in greater detail belowwith reference to FIG. 5. For example, the PTC thermistor R322 maycomprise part number B59807A0090A062, manufactured by EPCOS, Inc., whichhas a maximum nominal resistance of approximately 400Ω. A fault voltageV_(FAULT) is generated across the series combination of the PTCthermistor R322 and the output capacitor C_(OUT) and has a magnitudeapproximately equal to the magnitude of the DC supply voltage V_(CC)during normal operating conditions (i.e., in absence of a faultcondition).

The on-state power supply 220 comprises a control circuit 330, whichoperates, during normal operation, to render the FETs Q312, Q314non-conductive to temporarily and briefly block the load current I_(L).This allows the output capacitor C_(OUT) to conduct the load currentI_(L) and to thus charge for at least a portion of a line cycle of theAC power source 102 when the relay 210 in conductive. Accordingly, themagnitude of the DC supply voltage V_(CC) increases when thebidirectional semiconductor switch 310 is non-conductive and decreaseswhen the bidirectional semiconductor switch is conductive. Specifically,the control circuit 330 renders the FETs Q312, Q314 non-conductive whenthe magnitude of the DC supply voltage V_(CC) drops to the minimumsupply voltage V_(CC-MIN) (i.e., approximately five volts) and rendersthe FETs conductive when the magnitude of the DC supply voltage V_(CC)rises to the maximum supply voltage V_(CC-MAX) (i.e., approximately sixvolts).

The control circuit 330 of the on-state power supply 260 comprises, forexample, an analog circuit having a comparator U332 for controlling whenthe FETs Q312, Q314 are conductive in response to the magnitude of theDC supply voltage V_(CC). A resistor divider comprising two resistorsR334, R336 is coupled between the DC supply voltage V_(CC) and circuitcommon and provides a scaled voltage that is representative of themagnitude of the DC supply voltage V_(CC) to the positive terminal ofthe comparator U332. The resistors R334, R336 may have, for example,resistances of approximately 40.2 kΩ and 11 kΩ, respectively.

The control circuit 330 comprises a shunt regulator D338 (e.g., partnumber TLV431 manufactured by Texas Instruments) having a cathodeconnected to the DC supply voltage V_(CC) through a resistor R340 (e.g.,having a resistance of approximately 11 kΩ). The cathode of the shuntregulator D338 is coupled to the reference terminal of the shuntregulator and to the negative terminal of the comparator U332, such thata fixed reference voltage (e.g., approximately 1.24 V) is provided atthe negative terminal. A resistor R342 (e.g., having a resistance ofapproximately 47 kΩ) is coupled between the positive terminal and theoutput terminal of the comparator U332 for providing some hysteresis inthe operation of the on-state power supply 220. The output of thecomparator U332 is pulled up to the DC supply voltage V_(CC) through aresistor R344 (e.g., having a resistance of approximately 11 kΩ). Whenthe scaled voltage at the positive terminal of the comparator U332 isless than the fixed reference voltage (i.e., 1.24 V) at the negativeterminal of the comparator, the output terminal of the comparator U332is driven low, so as to render the FETs Q312, Q314 non-conductive aswill be described below. Alternatively, the control circuit 330 of theon-state power supply 220 could comprise a digital circuit thatincludes, for example, a microprocessor, a PLD, an ASIC, an FPGA, orother suitable type of integrated circuit. The comparator U332 maycomprise part number LM2903 manufactured by National SemiconductorCorporation.

The output of the comparator U332 is coupled to the base of an NPNbipolar junction transistor Q345 via a resistor R346 (e.g., having aresistance of approximately 22 kΩ). The collector of the transistor Q345is coupled to the DC supply voltage V_(CC) via two resistors Q348, Q350(e.g., having resistances of 100 kΩ and 22 kΩ, respectively). The baseof a PNP bipolar junction transistor Q352 is coupled to the junction ofthe two resistors Q348, Q350. The collector of the transistor Q352 iscoupled to the gates of the FETs Q312, Q314 via two respective gateresistors R354, R356 (e.g., both having a resistance of approximately8.2 kΩ). When the output terminal of the comparator U332 is pulled hightowards the DC supply voltage V_(CC), the transistors Q345, Q352 areboth rendered conductive. Accordingly, the DC supply voltage V_(CC) iscoupled to the gates of the FETs Q312, Q314 via the respective gateresistors R354, R356, thus rendering the FETs conductive. When theoutput terminal of the comparator U332 is driven low (i.e.,approximately at circuit common) and the transistors Q345, Q352 arerendered non-conductive, the gate capacitances of the gates of the FETsdischarge through a resistor R358 (e.g., having a resistance ofapproximately 8.2 kΩ) and the FETs are rendered non-conductive.

FIG. 4A is a simplified diagram of example waveforms illustrating theoperation of the on-state power supply 220 when the lighting load 104 isa resistive load, such as an incandescent lamp, and the charging currentI_(CHRG) is asynchronous with respect to the frequency of the AC powersource 102. While the FETs Q312, Q314 are non-conductive, the DC supplyvoltage V_(CC) increases in magnitude (from the minimum supply voltageV_(CC-MIN) to the maximum supply voltage V_(CC-MAX)) during a chargingtime T_(CHRG). During the charging time T_(CHRG), the scaled voltage atthe positive terminal of the comparator U332 (which is representative ofthe magnitude of the DC supply voltage V_(CC)) is less than thereference voltage of the shunt regulator D338 at the negative terminal.When the magnitude of the DC supply voltage V_(CC) exceeds the maximumsupply voltage V_(CC-MAX), the output of the comparator U332 is drivenhigh towards the DC supply voltage V_(CC) and the FETs Q312, Q314 arerendered conductive (as shown by the gate voltages V_(G) in FIG. 4A). Atthis time, the voltage at the positive terminal of the comparator U332is pulled high towards the DC supply voltage V_(CC). Since the FETsQ312, Q314 are conductive, the magnitude of the DC supply voltage V_(CC)and the magnitude of the scaled voltage at the negative terminal of thecomparator U332 begin to decrease as the controller 214 and otherlow-voltage circuits of the electronic switch 110 draw current from theoutput capacitor C_(OUT).

When the magnitude of the DC supply voltage V_(CC) drops below theminimum supply voltage V_(CC-MIN), the scaled voltage at the positiveterminal of the comparator U332 becomes less than the reference voltageof the shunt regulator D338 at the negative terminal. The output of thecomparator U332 is driven low towards circuit common, and the FETs Q312,Q314 are rendered non-conductive, thus allowing the output capacitorC_(OUT) to charge and the DC supply voltage V_(CC) to increase inmagnitude during the charging time T_(CHRG). As a result of theoperation of the power supply 220, only a low-voltage drop (i.e.,approximately five volts) is developed across the power supply and theswitched hot voltage V_(SH) has only small “notches” (i.e., smallchanges in magnitude) when the output capacitor C_(OUT) is charging asshown in FIG. 4A. Note that the worst case charging time T_(CHRG) may beequal to approximately the period T_(HC) of a half cycle of the AC powersource 102 if the output capacitor C_(OUT) charges and discharges suchthat the magnitude of the DC supply voltage V_(CC) does not exceed themaximum supply voltage V_(CC-MAX).

FIG. 4B is a simplified diagram of example waveforms illustrating theoperation of the on-state power supply 220 when the load current I_(L)is non-sinusoidal (e.g., the lighting load 104 is a compact fluorescentlamp), and the charging current I_(CHRG) is synchronous with respect tothe frequency of the AC power source 102. As shown in FIG. 4B, thecharging current I_(CHRG) does not immediately begin flowing when themagnitude of the DC supply voltage drops below the minimum supplyvoltage V_(CC-MIN) even though the gate voltages V_(G) are driven lowand the FETs Q312, Q314 are rendered non-conductive. The chargingcurrent I_(CHRG) begins flowing when the lighting load 104 beginsconducting the load current I_(L), which occurs at approximately thesame time each half cycle, such that the charging current I_(CHRG) issymmetric with respect to the frequency of the AC power source 102. Onceagain, only a low-voltage drop is developed across the power supply 220and the switched hot voltage V_(SH) has only small notches when theoutput capacitor C_(OUT) is charging as shown in FIG. 4B.

Referring back to FIG. 3, the feedback control signal V_(FB), which isprovided to the controller 214, is generated at the collector of thetransistor Q345. Thus, the feedback control signal V_(FB) is the inverseof the gate voltage V_(G) shown in FIGS. 4A and 4B. When the transistorQ345 is conductive (i.e., the FETs Q312, Q314 are conductive and theoutput capacitor C_(OUT) is discharging), the feedback control signalV_(FB) is driven low towards circuit common (i.e., a logic low level).When the transistor Q345 is non-conductive (i.e., the FETs Q312, Q314are non-conductive and the output capacitor C_(OUT) is charging), thefeedback control signal V_(FB) is pulled up towards the DC supplyvoltage V_(CC) (i.e., a logic high level). When the controller 214 isready to render the relay 210 conductive or non-conductive, thecontroller may wait until the feedback control signal V_(FB) transitionsfrom high to low (i.e., the magnitude of the DC supply voltage V_(CC) isat the maximum supply voltage C_(CC-MAX)) before energizing either theSET coil or the RESET coil of the relay.

The controller 214 is operable to determine if the electronic switch 110is overloaded (i.e., if an overload condition is occurring) in responseto the charging time T_(CHRG) required to charge the output capacitorC_(OUT). For example, the electronic switch 110 may be overloaded if thelighting load 104 causes the load current I_(L) conducted through therelay 210 to have a magnitude of approximately eight amps. Specifically,the controller 214 is operable measure the length of the time periodbetween the low-to-high and high-to-low transitions of the feedbackcontrol signal V_(FB) (i.e., the length of the charging time T_(CHRG)when the output capacitor C_(OUT) is charging). As the magnitude of theload current I_(L) increases, the charging time T_(CHRG) required tocharge the output capacitor C_(OUT) decreases. Therefore, the controller214 is operable to compare the time period between the low-to-high andhigh-to-low transitions of the feedback control signal V_(FB) to apredetermined charging time threshold T_(CHRG-TH) (e.g., approximately85 μsec) to determine if an overload condition may be occurring.Specifically, the controller 214 determines that the overload conditionis occurring in response to detecting that a percentage (e.g., 10%) ofthe charging times T_(CHRG) are less than the predetermined chargingtime threshold, for example, if ten of the last one hundred time periodsbetween the low-to-high and high-to-low transitions of the feedbackcontrol signal V_(FB) are less than approximately 85 μsec. Thecontroller 214 opens the relay 210 when the overload condition isdetected. In addition, the controller 214 may blink the visual indicator114 in response to detecting the overload condition.

FIG. 5 is a simplified schematic diagram showing how the in-lineon-state power supply 220 is coupled to the latching relay 210 and thedrive circuit 216 for the bidirectional semiconductor switch 212 toprovide for fault detection and protection of the electronic switch 110.The SET coil of the relay 210 is coupled between the relay-set controlsignal V_(RLY-SET) and the DC supply voltage V_(CC). When the controller214 drives the relay-set control signal V_(RLY-SET) low to approximatelycircuit common, the mechanical switch of the relay 210 is renderedconductive. The RESET coil of the relay 210 is coupled between therelay-reset control signal V_(RLY-RESET) and the fault voltageV_(FAULT), which has a magnitude approximately equal to the magnitude ofthe DC supply voltage V_(CC) during normal operating conditions (i.e.,in absence of an over-temperature condition). The relay-reset controlsignal V_(RLY-RESET) is also coupled to the DC supply voltage V_(CC)through a diode D305. When the controller 214 drives the relay-resetcontrol signal V_(RLY-RESET) low to approximately circuit common duringnormal operating conditions, the mechanical switch of the relay 210 isrendered non-conductive.

If the output capacitor C_(OUT) were to fail shorted when the latchingrelay 210 is conductive, the temperatures of the FETs Q312, Q314 of theon-state power supply 220 may increase to undesirable levels. Accordingto an aspect of the present invention, when an over-temperaturecondition is detected in the FETs Q312, Q314 of the on-state powersupply 220, the electronic switch 110 controls the latching relay 210(e.g., to open the relay) in order to remove the over-temperaturecondition. Specifically, the PTC thermistor R322 is thermally coupled tothe FETs Q312, Q314, such that the resistance of the PTC thermistorincreases as the combined temperature of the FETs increases during theover-temperature condition, thus causing the fault voltage V_(FAULT) toincrease in magnitude. Since the series combination of the diode D305and the RESET coil of the relay 210 is coupled between the fault voltageV_(FAULT) and the DC supply voltage V_(CC) (i.e., in parallel with theoutput PTC thermistor R322), current begins to flow through the RESETcoil as the resistance of the PTC thermistor increases and the magnitudeof the fault voltage V_(FAULT) increases. The relay 210 is renderednon-conductive when the combined temperature of the FETs Q312, Q314increases above a predetermined temperature threshold T_(FAULT) (e.g.,approximately 90° F.). In other words, the relay 210 is renderednon-conductive when the fault voltage V_(FAULT) increases such that thevoltage across the RESET coil renders the relay 210 non-conductive.Accordingly, the current through the FETs Q312, Q314 is controlled tozero amps and the fault condition is removed (i.e., the temperatures ofthe FETs will decrease below the undesirable levels). The relay 210 isrendered conductive in response to the over-temperature conditionindependent of the magnitude of the relay-reset control signalV_(RLY-RESET). In addition, the relay 210 could be rendered conductivein response to an over-temperature condition in other circuits of theelectronic switch 110.

As shown in FIG. 5, the bidirectional semiconductor switch 212 isimplemented as a triac. The drive circuit 216 comprises an optocouplerU380 having an output phototriac coupled in series with the gate of thebidirectional semiconductor switch 212. When the output phototriac ofthe optocoupler U380 is conductive, the output phototriac conducts agate current through two resistors R382, R384 each half cycle of the ACpower source 102, thus rendering the bidirectional semiconductor switch216 conductive each half cycle. The resistors R382, R384 may both have,for example, resistances of approximately 100 Ω.

The optocoupler U380 also has an input photodiode having an anodecoupled to the rectified voltage V_(RECT) of the on-state power supply220. An NPN bipolar junction transistor Q385 is coupled in series withthe input photodiode of the optocoupler U380. The controller 214 iscoupled to the base of the transistor Q385 via a resistor R386 (e.g.,having a resistance of approximately 1 kΩ). When the transistor Q385 isrendered conductive, the transistor conducts a drive current through theinput photodiode of the optocoupler U380 and a resistor R388 (e.g.,having a resistance of approximately 330Ω), thus rendering the outputoptotriac and the bidirectional semiconductor switch 212 conductive.

According to another aspect of the present invention, when anover-current condition is detected in the in-line on-state power supply220, the electronic switch 110 uses the bidirectional semiconductorswitch 212 to remove the over-current condition. The over-currentcondition may be caused by an inrush current conducted through the relay210, for example, when the lighting load 104 is a capacitive load, suchas a screw-in compact fluorescent lamp or an electronic low-voltage(ELV) lighting load. For example, the inrush current may have amagnitude greater than approximately three hundred amps and last forapproximately two milliseconds as defined by the NEMA 410 Standardpublished by the National Electrical Manufacturers Association (NEMA).To protect the on-state power supply 220 from the over-currentcondition, the bidirectional semiconductor switch 212 is renderedconductive when the current through the over-current detect resistorR320 of the on-state power supply 220 exceeds a predetermined currentthreshold I_(FAULT) (e.g., approximately forty amps). At this time, thevoltage across the on-state power supply 220 is reduced to approximatelythe on-state voltage of the bidirectional semiconductor switch 212(e.g., approximately one volt), which causes the power supply to stopcharging the output capacitor C_(OUT), and eliminates the over-currentcondition.

Referring back to FIG. 5, the over-current detect resistor R320 of theon-state power supply 220 is coupled in parallel with the seriescombination of the input photodiode of the optocoupler U380, a diodeD390, and a resistor R392 (e.g., having a resistance of approximately47Ω). When the current through the over-current detect resistor R320exceeds the predetermined current threshold I_(FAULT), the voltagegenerated across the series combination of the input photodiode of theoptocoupler U380, the diode D390, and the resistor R392 causes theoutput phototriac of the optocoupler to be rendered conductive.Accordingly, the bidirectional semiconductor switch 212 is renderedconductive and the over-current condition is eliminated. Since thebidirectional semiconductor switch 212 is a triac, the bidirectionalsemiconductor switch becomes non-conductive at the end of the half cyclewhen the current through the bidirectional semiconductor switch drops toapproximately zero amps. The bidirectional semiconductor switch 212 willbe rendered conductive once again during the next half cycle if theover-current condition remains.

FIG. 6 is a simplified flowchart of a button procedure 400 executed bythe controller 214 of the electronic switch 110 is response to anactuation of the switch S224 at step 410. The controller 214 uses twotimers, e.g., a relay timer and a bidirectional semiconductor switch(BSS) timer, to control when the relay 210 and the bidirectionalsemiconductor switch 212 become conductive and non-conductive. When therelay timer expires, the controller 214 executes a relay timer procedure600 to render the relay 210 conductive if the lighting load 104 is offand to render the relay non-conductive if the lighting load is on (aswill be described in greater detail below with reference to FIG. 8).When the BSS timer expires, the controller 214 executes a BSS timerprocedure 700 to control the bidirectional semiconductor switch 212 tobecome conductive if the lighting load 104 is off and to becomenon-conductive if the lighting load is on (as will be described ingreater detail below with reference to FIG. 9). The controller 214executes a received keypad message procedure (not shown), which issimilar to the button procedure 400, in response to receiving an oncommand (when the on button 122 is actuated) and an off command (whenthe off button 124).

Referring to FIG. 6, if the lighting load 104 is off at step 412, thecontroller 214 initializes the BSS timer to a BSS-turn-on timet_(BSS-ON), and starts the BSS timer decreasing in value with respect totime at step 414. The controller 214 then initializes the relay timer toa relay-turn-on time t_(RLY-ON), and starts the relay timer decreasingin value with respect to time at step 416, before the button procedure400 exits. For example, the BSS-turn-on time t_(BSS-ON) may beapproximately zero milliseconds and the relay-turn-on time t_(RLY-ON)may be approximately thirty milliseconds, such that the bidirectionalsemiconductor switch 212 will be rendered conductive before the relay210 is rendered conductive. If the lighting load 104 is on at step 412,the controller 214 immediately renders the bidirectional semiconductorswitch 212 conductive at step 418. The controller 214 then initializesthe relay timer to a relay-turn-off time t_(RLY-OFF), and starts therelay timer decreasing in value with respect to time at step 420.Finally, the controller 214 initializes the BSS timer to a BSS-turn-offtime t_(BSS-OFF), and starts the BSS timer decreasing in value withrespect to time at step 422, before the button procedure 400 exits. Forexample, the relay-turn-off time t_(RLY-OFF) may be approximately thirtymilliseconds and the BSS-turn-off time t_(BSS-OFF) may be approximatelysixty milliseconds, such that the relay 210 will be renderednon-conductive before the bidirectional semiconductor switch 212 becomesnon-conductive.

FIG. 7 is a simplified flowchart of a received occupancy messageprocedure 500 executed by the controller 214 of the electronic switch110 in response to receiving a digital message from one of the occupancysensors 130 via the RF signals 106 at step 510. The controller 214 keepstrack of the states of the occupancy sensor 130 to which the electronicswitch 110 is assigned in response to the digital messages received fromthe occupancy sensors. Specifically, if the controller 214 receives anoccupied-take-action command or an occupied-no-action command from anoccupancy sensor 130, the controller marks the serial number of theoccupancy sensor as “occupied” in the memory 228. If the controller 214receives a vacant command from the occupancy sensor 130, the controllermarks the serial number of the occupancy sensor as “vacant” in thememory 228. The controller waits for a vacant command from all of theoccupancy sensors to which the electronic switch 110 is assigned beforeturning off the lighting load 104.

Referring to FIG. 7, after receiving the digital message at step 510,the controller 214 first determines whether the serial number providedin the received digital message is stored in the memory 228 at step 512.If not, the controller 214 does not process the received digital messageand the received occupancy message procedure 500 exits. If the serialnumber of the received digital message is stored in the memory 228 atstep 512 and the received digital message is an occupied-take-actioncommand at step 514, the controller 214 determines if any of the serialnumbers stored in the memory 228 are marked as occupied at step 516 todetermine if the space is occupied or vacant. If there are no serialnumbers marked as occupied at step 516 (i.e., the space has just becomeoccupied), the controller 214 turns on the lighting load 104 byinitializing and starting the BSS timer (using the BSS-turn-on timet_(BSS-ON)) at step 518, and initializing and starting the relay timer(using the relay-turn-on time t_(RLY-ON)) at step 520. The controller214 then marks the serial number of the received digital message asoccupied at step 522 and the received message procedure 510 exits. Ifthere are serial numbers marked as occupied at step 516 (i.e., the spaceis occupied), the controller 214 marks the serial number of the receiveddigital message as occupied at step 522, before the received occupancymessage procedure 500 exits.

If the received digital message is an occupied-no-action command at step524, the controller 214 does not adjust the amount of power delivered tothe lighting load 104. The controller 214 simply marks the serial numberas occupied at step 522 and the received occupancy message procedure 500exits. If the received digital message is a vacant command at step 526,the controller 214 marks the serial number as vacant at step 528. If anyof the serial numbers are still marked as occupied at step 530 (i.e.,the space is still occupied), the received occupancy message procedure500 simply exits. However, if all of the serial numbers are marked asvacant at step 530 (i.e., the space is now vacant), the controller 214controls the lighting load 104 off by immediately rendering thebidirectional semiconductor switch 212 conductive at step 532,initializing and starting the relay timer (using the relay-turn-off timet_(RLY-OFF)) at step 534, and initializing and starting the BSS timer(using the BSS-turn-off time t_(BSS-OFF)) at step 536, before thereceived occupancy message procedure 500 exits.

FIG. 8 is a simplified flowchart of a relay timer procedure 600 executedby the controller 214 when the relay timer expires at step 610. First,the controller 214 waits until the feedback control signal V_(FB)transitions from high to low at step 612 indicating that the magnitudeof the DC supply voltage V_(CC) is equal to the maximum supply voltageV_(CC-MAX). When the controller 214 detects that the feedback controlsignal V_(FB) has transitioned from high to low at step 612, thecontroller immediately renders the relay 210 conductive ornon-conductive depending upon the present state of the lighting load104. If the lighting load 104 is off at step 614, the controller 214renders the relay 210 conductive at step 616 by conducting currentthrough the SET coil of the relay and the relay timer procedure 600exits. If the lighting load 104 is off at step 614, the controller 214renders the relay 210 non-conductive at step 618 by conducting currentthrough the RESET coil and the relay timer procedure 600 exits.

FIG. 9 is a simplified flowchart of a BSS timer procedure 700 executedby the controller 214 when the BSS timer expires at step 710. If thelighting load 104 is off at step 712, the controller 214 controls thedrive circuit 216 to render the bidirectional semiconductor switch 212conductive at step 714 and illuminates the visual indicator 214 at step716, before the BSS timer procedure 700 exits. If the lighting load 104is off at step 712, the controller 214 controls the drive circuit 216such that the bidirectional semiconductor switch 212 becomesnon-conductive at step 718. The controller 214 then controls the visualindicator 214 to be off at step 720 and the BSS timer procedure 700exits.

FIG. 10 is a simplified flowchart of an overload detection procedure 800executed by the controller 214 when the feedback control signal V_(FB)transitions from high to low or low to high at step 810. If the detectedtransition of the feedback control signal V_(FB) is a low-to-hightransition at step 812, the controller 214 initializes a timer (e.g., tozero μsec) and starts the timer increasing in value with respect to timeat step 814, before the overload detection procedure 800 exits. If thedetected transition of the feedback control signal V_(FB) is ahigh-to-low transition at step 812, the controller 214 stores thepresent value of the timer at step 816. If the timer value is greaterthan the predetermined charging time threshold T_(CHRG-TH) (i.e.,approximately 85 μsec) at step 818, the overload detection procedure 800simply exits. However, if the timer value is less than or equal toapproximately the predetermined charging time threshold T_(CHRG-TH) atstep 818, the controller 214 determines if an overload condition isoccurring at step 820. Specifically, the controller 214 determines atstep 820 if a percentage (e.g., 10%) of the most recently stored timervalues (from step 816) are less than the predetermined charging timethreshold, for example, if ten of the last one hundred stored timervalues are less than approximately 85 μsec. If the controller 214 doesnot detect the overload condition at step 820, the overload detectionprocedure 800 simply exits. Otherwise, if the controller 214 detects theoverload condition at step 820, the controller 214 renders the relay 210non-conductive at step 822 and blinks the visual indicator 114 at step824, before the overload detection procedure 800 exits.

While the present invention has been described with reference to theelectronic switch 110 controlling the power delivered to a connectedlighting load, the concepts of the present invention could be used inany type of control device of a load control system, such as, forexample, a dimmer switch for adjusting the intensity of a lighting load(such as an incandescent lamp, a magnetic low-voltage lighting load, anelectronic low-voltage lighting load, and a screw-in compact fluorescentlamp), a remote control, a keypad device, a visual display device, acontrollable plug-in module adapted to be plugged into an electricalreceptacle, a controllable screw-in module adapted to be screwed intothe electrical socket (e.g., an Edison socket) of a lamp, an electronicdimming ballast for a fluorescent load, and a driver for alight-emitting diode (LED) light source, a motor speed control device, amotorized window treatment, a temperature control device, anaudio/visual control device, or a dimmer circuit for other types oflighting loads, such as, magnetic low-voltage lighting loads, electroniclow-voltage lighting loads, and screw-in compact fluorescent lamps.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A two-wire electronic switch for controlling thepower delivered from an AC power source to an electrical load, theelectronic switch comprising: a latching relay adapted to be coupled inseries electrical connection between the source and the load, thelatching relay arranged to conduct a load current through the load whenthe relay is conductive; a controller configured to control the relay tobe conductive and non-conductive to turn the load on and off,respectively; an output capacitor arranged to develop a DC supplyvoltage for powering the controller; and an in-line power supply coupledin series electrical connection with the relay, the in-line power supplyfurther coupled to the output capacitor for generating the DC supplyvoltage across the output capacitor when the relay is conductive, thepower supply configured to conduct the load current through the outputcapacitor for at least a portion of a line cycle of the AC power sourcewhen the relay is conductive; wherein the relay is renderednon-conductive in response to an over-temperature condition in theelectronic switch.
 2. The electronic switch of claim 1, wherein thepower supply comprises a bidirectional semiconductor switch coupled inseries with the relay and in parallel with the output capacitor, thepower supply configured to render the bidirectional semiconductor switchnon-conductive to charge the output capacitor when the relay isconductive.
 3. The electronic switch of claim 2, wherein the controlleris configured to provide a relay-set control signal to a SET coil of therelay to render the relay conductive, and a relay-reset control signalto a RESET coil of the relay to render the relay non-conductive, thepower supply further comprising a thermistor responsive to a temperatureof the power supply, the thermistor electrically coupled to the RESETcoil of the relay for rendering the relay non-conductive in response toan over-temperature condition in the power supply.
 4. The electronicswitch of claim 3, wherein the thermistor comprises a PTC thermistorthermally coupled to the bidirectional semiconductor switch of the powersupply.
 5. The electronic switch of claim 4, wherein the PTC thermistoris coupled in series electrical connection with the output capacitor ofthe power supply, and the voltage across the series combination of theoutput capacitor and the PTC thermistor is electrically coupled to theRESET coil of the relay, the controller configured to control therelay-reset control signal to render the relay non-conductive in absenceof the over-temperature condition in the power supply; and wherein thevoltage across the series combination of the output capacitor and thePTC thermistor increases during the over-temperature condition in thepower supply, and the relay is rendered non-conductive independent ofthe magnitude of the relay-reset control signal.
 6. The electronicswitch of claim 2, wherein the power supply further comprises a controlcircuit coupled to the bidirectional semiconductor switch for renderingthe bidirectional semiconductor switch conductive and non-conductive,the control circuit responsive to the magnitude of the DC supply voltageto render the bidirectional semiconductor switch conductive when themagnitude of the DC supply voltage reaches a maximum DC supply voltagethreshold.
 7. The electronic switch of claim 6, wherein the controlcircuit of the power supply is configured to render the bidirectionalsemiconductor switch non-conductive when the magnitude of the DC supplyvoltage drops to a minimum DC supply voltage threshold.
 8. Theelectronic switch of claim 2, further comprising: an off-state powersupply coupled in parallel with the series combination of the relay andthe in-line power supply, the off-state power supply coupled to theoutput capacitor for controlling when the output capacitor charges togenerate the DC supply voltage across the output capacitor when therelay is non-conductive.
 9. The electronic switch of claim 8, furthercomprising: a communication circuit configured to receive digitalmessages; wherein the controller is configured to turn the load on andoff in response to the digital messages received via the communicationcircuit.
 10. The electronic switch of claim 1, wherein the bidirectionalsemiconductor switch of the power supply comprises two FETs inanti-series connection.
 11. The electronic switch of claim 1, furthercomprising: a triac coupled in parallel with the series combination ofthe relay and the power supply, the controller configured to turn on theload by first rendering the triac conductive and then rendering therelay conductive, the controller configured to turn off the load byfirst rendering the relay non-conductive and then rendering the triacnon-conductive; wherein the triac is rendered conductive in response toan over-current condition in the output capacitor of the power supply.12. A two-wire electronic switch for controlling the power deliveredfrom an AC power source to an electrical load, the electronic switchcomprising: a latching relay adapted to be coupled in series electricalconnection between the source and the load for turning the load on andoff; a first bidirectional semiconductor switch coupled in parallelelectrical connection with the relay, the first bidirectionalsemiconductor switch comprising a control input; a controller configuredto turn on the load by first rendering the first bidirectionalsemiconductor switch conductive and then rendering the relay conductive,the controller configured to turn off the load by first rendering therelay non-conductive and then rendering the first bidirectionalsemiconductor switch non-conductive; an output capacitor arranged todevelop a DC supply voltage for powering the controller; and an in-linepower supply coupled in series electrical connection with the relay, thefirst bidirectional semiconductor switch being electrically connected inparallel with the series combination of the relay and the power supply,the in-line power supply being coupled to the output capacitor forgenerating the DC supply voltage across the output capacitor when therelay is conductive, the power supply being configured to conduct theload current through the output capacitor for at least a portion of aline cycle of the AC power source when the relay is conductive; whereinthe first bidirectional semiconductor switch is rendered conductive inresponse to an over-current condition in the output capacitor of thepower supply.
 13. The electronic switch of claim 12, wherein the powersupply comprises a second bidirectional semiconductor switchelectrically connected in series with the relay and in parallel with theoutput capacitor, the power supply being configured to render the secondbidirectional semiconductor switch non-conductive to charge the outputcapacitor when the relay is conductive.
 14. The electronic switch ofclaim 13, further comprising: a drive circuit coupled between thecontroller and the control input of the first bidirectionalsemiconductor switch, the drive circuit being configured to render thefirst bidirectional semiconductor switch conductive in response to acontrol signal provided by the controller.
 15. The electronic switch ofclaim 14, wherein the power supply comprises a resistor coupled inseries with the output capacitor, the resistor being coupled to thedrive circuit, the drive circuit being configured to render the firstbidirectional semiconductor switch conductive in response to the currentthrough the resistor exceeding a predetermined current threshold. 16.The electronic switch of claim 14, wherein the first bidirectionalsemiconductor switch comprises a triac.
 17. The electronic switch ofclaim 13, wherein the latching relay is coupled to the power supply, andthe relay is rendered non-conductive in response to an over-temperaturecondition in the power supply.
 18. The electronic switch of claim 17,wherein the controller is configured to provide a relay-set controlsignal to a SET coil of the relay for rendering the relay conductive,and a relay-reset control signal to a RESET coil of the relay forrendering the relay non-conductive, the power supply further comprisinga PTC thermistor thermally coupled to the second bidirectionalsemiconductor switch of the power supply, the PTC thermistor beingcoupled in series electrical connection with the output capacitor of thepower supply, the voltage across the series combination of the outputcapacitor and the PTC thermistor electrically being coupled to the RESETcoil of the relay, the controller being configured to control therelay-reset control signal to render the relay non-conductive in absenceof the over-temperature condition in the power supply; and wherein thevoltage across the series combination of the output capacitor and thePTC thermistor increases during the over-temperature condition in thepower supply, and the relay is rendered non-conductive independent ofthe magnitude of the relay-reset control signal.
 19. The electronicswitch of claim 13, wherein the power supply further comprises a controlcircuit coupled to the second bidirectional semiconductor switch forrendering the second bidirectional semiconductor switch conductive andnon-conductive, the control circuit being responsive to the magnitude ofthe DC supply voltage to render the second bidirectional semiconductorswitch conductive when the magnitude of the DC supply voltage reaches amaximum DC supply voltage threshold.
 20. The electronic switch of claim19, wherein the control circuit of the power supply is configured torender the second bidirectional semiconductor switch non-conductive whenthe magnitude of the DC supply voltage drops to a minimum DC supplyvoltage threshold.
 21. A two-wire electronic switch for controlling thepower delivered from an AC power source to an electrical load, theelectronic switch comprising: a latching relay adapted to be coupled inseries electrical connection between the source and the load for turningthe load on and off; a first bidirectional semiconductor switch coupledin parallel electrical connection with the relay, the firstbidirectional semiconductor switch comprising a control input; acontroller configured to turn on the load by first rendering the firstbidirectional semiconductor switch conductive and then rendering therelay conductive, the controller configured to turn off the load byfirst rendering the relay non-conductive and then rendering the firstbidirectional semiconductor switch non-conductive; an output capacitorarranged to develop a DC supply voltage for powering the controller; andan in-line power supply coupled in series electrical connection with therelay, the first bidirectional semiconductor switch being electricallyconnected in parallel with the series combination of the relay and thepower supply, the in-line power supply being coupled to the outputcapacitor for generating the DC supply voltage across the outputcapacitor when the relay is conductive, the power supply comprising asecond bidirectional semiconductor switch electrically connected inseries with the relay and in parallel with the output capacitor, thepower supply being configured to render the second bidirectionalsemiconductor switch non-conductive to charge the output capacitor whenthe relay is conductive; wherein the first bidirectional semiconductorswitch is rendered conductive in response to an over-current conditionin the output capacitor of the power supply, and the relay is renderednon-conductive in response to an over-temperature condition in the powersupply.